This invention relates generally to a method for determining a condition of an exhaust gas recirculation (EGR) system and, more particularly, to a method for determining a condition of an EGR system as a function of at least one temperature.
Exhaust gas recirculation is a technique commonly used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. This technique has proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. The exhaust gas recirculation technique primarily involves the recirculation of exhaust gas by-products into the intake air supply of the internal combustion engine. This exhaust gas thus reintroduced into the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxide. Furthermore, the exhaust gases typically contain a portion of unburned hydrocarbon which is burned on its reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
It is important that the EGR system functions properly at all times, thus reducing the emission of these undesirable by-products into the atmosphere, and allowing the internal combustion engine to operate at peak efficiency. Attempts have been made, with some limited degree of success, to monitor conditions of EGR systems to determine proper operation of the system. For example, in U.S. Pat. No. 5,727,533, Bidner et al. disclose a method and apparatus, using a temperature sensor at the intake manifold of an internal combustion engine, to monitor the temperature of the combined air and EGR gases as they enter the cylinders. In U.S. Pat. No. 4,967,717, Miyazaki et al. use a temperature sensor at the intake manifold and an additional temperature sensor at the air intake passage of the engine to compare the change in temperature from the air intake to the intake manifold, i.e., before and after the EGR gases are introduced into the air stream. In U.S. Pat. No. 4,870,941, Hisatomi uses a temperature sensor located in the EGR passage upstream of the EGR valve to determine the temperature of the exhaust gases prior to entering the EGR valve. Each of these attempts to monitor the condition of an EGR system are limited to those systems used for small engines; that is, the EGR systems are relatively simple in that they do not require the addition of cooling systems or air pressure compensation such as would be needed on larger diesel engines.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably re-introduced to the intake air stream downstream of the compressor and air-to-air aftercooler. Reintroducing the exhaust gas downstream of the compressor and air-to-air aftercooler is preferred due to the reliability and maintainability concerns that arise should the exhaust gas be passed through the compressor and aftercooler. However, at some engine operating conditions, there is a pressure differential between the intake manifold and the exhaust manifold which essentially prevents many conventional EGR systems from being utilized. For example, at high speed, high load conditions in a turbocharged engine, the exhaust gas does not readily flow from the exhaust manifold to the intake manifold.
With the increased complexity of EGR systems on larger diesel engines, including engines with turbochargers, proper operation of the EGR system is even more important. However, monitoring the condition of the EGR system becomes more complex and difficult with the additional components required for the system.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for determining a condition of an exhaust gas recirculation (EGR) system for an internal combustion engine is disclosed. The method includes the steps of setting an EGR valve located on the EGR system to a first position, determining a first temperature value at a location on the EGR system, setting the EGR valve to a second position, determining a second temperature value at the location, and determining a condition of the EGR system as a function of the difference between the first and second temperature values.
In another aspect of the present invention a method for determining a condition of an exhaust gas recirculation (EGR) system for an internal combustion engine is disclosed. The method includes the steps of holding an EGR valve located on the EGR system at an open position, setting a cold side valve located on the EGR system to a first position, determining a first temperature value at a location on the EGR system, setting the cold side valve to a second position, determining a second temperature value at the location, and determining a condition of the EGR system as a function of the difference between the first and second temperature values.
In yet another aspect of the present invention a method for determining a flow coefficient of an exhaust gas recirculation (EGR) system for an internal combustion engine having at least one cylinder, an intake manifold, and an exhaust manifold is disclosed. The method includes the steps of determining a percent of EGR (%EGR) being recirculated as a function of temperatures at the intake and exhaust manifolds, determining a mass airflow through the cylinder, determining a mass airflow through an EGR valve located in the EGR system, determining a manifold pressure differential between the intake manifold and the exhaust manifold, and determining the EGR flow coefficient as a function of the mass airflow through the EGR valve and the manifold pressure differential.